Sound transduction can occur where high strain is induced in piezoelectric or magnetostrictive materials. In the case of piezoelectric and magnetic methods of transduction, a large strain is produced when these materials are driven by very high applied electric or magnetic field. This often requires a direct electric or magnetic field introduced to the transducer placed in a contact with the media. This limitation of required high voltage or current must be overcome by using the thermo-acoustic or optoacoustic transduction mechanism to achieve remote, contactless generation of acoustic waves.
The current state of the art in acoustic transduction utilizes piezoelectric ceramic materials that show high energy conversion efficiency. These materials directly convert a voltage (electric field) to displacement and therefore require a moderate amount of power. In recent years the development of relaxor ferroelectric single crystals has led to successive improvements in the transduction coupling in single crystals compared to piezoceramics making them extremely promising for sound generation, actuation, ultrasonic sensors for medical and naval applications (see refs. 1-3).
A need exists for new materials suitable for compact and robust acoustic sources, hydrophones, vector sensors and acoustic transducers. Furthermore, there is the need for direct electrical connection and control, requiring power at the transducer that severely limits applications of such transducers in hard to access or other remote locations.